A plasma display panel, adopting an AC surface-discharge method, comprises a front plate having plural display electrodes formed of scan electrodes and sustain electrodes, a back plate having plural address electrodes placed to intersect with the display electrodes at right angles. The front plate confronts the back plates such that a discharge space is formed in between, and the circumference of those two plates is sealed together. The discharge space is filled with discharge gas such as neon and xenon. The display electrodes are covered with a dielectric layer, and on top of that a protective layer is formed. The protective layer is generally made of highly resistive material, such as magnesium oxide (MgO), against sputtering for protecting the dielectric layer from ion-impact generated by discharge. Respective display electrodes form one line, and discharge cells are formed at intersections of the display electrodes and the address electrodes.
In the PDP discussed above, one field ( 1/60 seconds) of a video signal is formed of plural sub-fields having weighting of luminance, every sub-field has an address period and a sustain period. During the address period, data is addressed by generating address-discharge at a discharge cell which is to be lighted with each one of lines scanned sequentially. During the sustain period, discharges are initiated the number of times corresponding to the weighting of luminance at the discharge cell, to which data has been addressed during the address period, so that the cell is lit.
In the case of displaying a video of television broadcasting, all the operations of respective sub-fields should be completed within one field. Since the discharge cells are more densely populated on a screen recently, the number of scanning lines increases, so that address-discharge at each line should be done within a shorter period. In other words, during the address period, a pulse having a narrower width is applied to scan electrodes and address electrodes in order to generate address-discharge, so that a high speed driving should be carried out. However, since the discharge takes place with a delay from a rise of a pulse, i.e. there is a discharge-delay, the probability of completing a discharge during a pulse application becomes lower. Therefore, data cannot be addressed to discharge cells to be lit, so that a lighting defect sometimes occurs, which results in lowering the display quality.
A principal factor causing the foregoing discharge delay can be this: an initial electron working as a trigger at starting discharge becomes resistant to emission from the protective layer to the discharge space. The protective layer thus becomes a target of study for improving the display quality.
An improvement of electron emission from a protective layer is disclosed in Japanese Patent Application Non-Examined Publication No. H10-334809, namely, silicon is added to a protective layer made of MgO, so that an emission amount of secondary electrons increases for improving the display quality.
However, the protective layer made of MgO and Si substantially changes its capacity of emitting electrons depending on its temperature, so that the discharge-delay time also greatly changes. As a result, an ambient temperature of a PDP actually changes the display quality.